1. Field of the invention
The present invention relates to a control system for an internal combustion engine of a vehicle with an automatic transmission, and more specifically, to an output control of the engine in connection with a shift operation in the automatic transmission.
2. Description of the Prior Art
In a vehicle provided with an automatic transmission, there have been various proposals for reducing a torque shock or jolt through a shift operation from one gear stage to another in the automatic transmission. In a control system disclosed in U.S. Pat. No. 4,226,447, an ignition timing of the engine is controlled in accordance with a vehicle speed as a shift operation occurs so that an engine output power or torque is changed to reduce the torque shock due to the shift operation. U.S. Pat. Nos. 4,355,550, 4,370,903 and 4,403,527 disclose similar control systems.
In controlling the engine output during the shift operation, it should be noted that there is produced a time lag from a generation of a control signal for the shift operation to an actual initiation of the shift operation. In order to reduce the torque shock due to the shift operation effectively, it is desirable that the engine output control be made corresponding to the actual shift operation.
In view of this, the conventional ignition timing output control is adapted to be initiated to control the engine output torque after a predetermined time period from the generation of the control signal for the shift operation so that the engine output control occurs in synchronism with an actual shift operation.
It should, however, be noted that the time lag from the generation of the control signal for the shift operation to the actual initiation of the shift operation varies, depending on a vehicle operating condition such as engine speed, engine load defined by a parameter such as a throttle opening, intake gas amount and the like, line hydraulic pressure in the transmission, gear stages involved in the shift operation and the like.
Specifically, a viscosity of a hydraulic fluid or oil in the transmission affects greatly the time lag, since the shift operation is made in a manner such that a specific gear stage is established by switching power transmitting path in the transmission by virtue of the hydraulic fluid. Thus, where the viscosity of the hydraulic fluid is high, the shift operation may take long and become unstable. As a result, the engine output control may not correspond to the actual shift operation. This means that the torque shock due to the shift operation cannot be suppressed effectively because of the untimely engine output control. Moreover, the engine output control may deteriorate controllability (for example an acceleration property ) of the vehicle under the vehicle operating condition where the temperature of the hydraulic fluid is low.